The present invention relates to a novel ceramic-glass composite material and a method for the preparation thereof. More particularly, the invention relates to a ceramic-glass composite material having usefulness as a material of electronic parts for attenuation of noise components in the GHz frequency range and a method for the preparation of such a material.
It is a trend in the technological field of electronic instruments in recent years that devices or parts are mounted on the instrument in an overcrowding density resulting in an explicit problem of interference between devices and radiation of noises.
Since noises are higher harmonics of the signals under use, noises can be effectively reduced by suppressing the higher harmonics. While it is known that beads by using certain magnetic ferrite material serve for this purpose by utilizing the high-frequency absorption of ferrites, such a material hardly exhibits attenuation in the signal range so that the effect of noise attenuation is accomplished by the absorption only in the ranges of the higher harmonics.
On the other hand, it is also known to prevent interference by shielding a region of the circuit with a metal plate. By this means, namely, noise components such as higher harmonics are shielded from the other blocks of the circuit so as to prevent adverse influences thereof.
Further, it is practiced to form a low-pass filter by means of an LC resonance circuit so as to prevent propagation of noises to the further stages. The noise component prevented from propagation by a resonance circuit, however, is not actually reduced but is merely reflected back to the former stages sometimes resulting in an undesirable phenomenon of oscillation and the like in the circuit.
While various methods are known as described above for suppression of noises, the most preferable is a method of absorption of unnecessary noise components, for example, by the use of ferrite beads.
FIG. 1 of the accompanying drawing is a perspective view illustrating a typical examples of conventional ferrite beads having a structure in which a block 1 of a hexagonally crystalline ferrite is provided with penetrating holes 2,2 and a silver conductor is bake-bonded to each penetrating hole 2. Outer electrodes 4,4 are further provided. In this device, the noise component is suppressed in the signals passing the device. See Japanese Patent Kokai 3-161910.
Alternatively, a device is known by using a spinel ferrite such as NiCuZnFe.sub.2 O.sub.4. As is illustrated in FIG. 2 by a perspective view, a ferrite block 1 of a magnetic ceramic material capable of being sintered at about 900.degree. C. is provided with a penetrating hole 2, which is integrally sintered in combination jointly with an internal conductor of silver to form a coil-formed conductor 3 within a sintered ceramic body having external electrodes 4,4. In this way, the line length pertaining to the loss can be increased and an increased impedance can be obtained so that the loss in the material can be efficiently utilized and, as a consequence, the device can be rendered compact.
In the spinel ferrites, however, the so-called Snake's critical line exists between the frequency and the complex magnetic permeability resulting in disappearance of the magnetism at a frequency of 2 GHz or higher not to fully exhibit the effect of noise suppression. Accordingly, suppression of noise at a higher frequency is usually under-taken by means of shielding with a metal plate or by using a low-pass filter.
While the hexagonal ferrite can be used within a high frequency range exceeding the frequency limit of the spinel ferrites, the sintering temperature thereof in a typical procedure is about 1250.degree. C. to exceed the melting point of silver so that cofiring treatment thereof, which is required in the preparation of the ferrite beads having a structure shown in FIG. 2, can be undertaken only with a great difficulty. Further, the hexagonal ferrites have a low resistivity of about 10.sup.5 ohm.multidot.cm so that troubles of short-circuiting are frequently encountered in the metal plating treatment for the preparation of chip parts.
With an object to decrease the disadvantageously high sintering temperature of the conventional hexagonal ferrites, a proposal is made in Japanese Patent Kokai 9-167703 for a hexagonal ferrite containing one kind or more of alkaline earth metal elements, lead and/or copper, iron and oxygen. The performance of this ferrite material, however, cannot be estimated because the resistivity of the ferrite material is not reported there.
The inventors have directed their attention to and conducted investigations on a composite material, as a material for the above mentioned applications, consisting of a matrix phase of a glass material and a dispersed phase of a ferrite, which is a kind of ceramic-glass composite materials under development in recent years including, for example, an alumina-glass composite as a material of multilayer capacitors reported by Uchikoba, et al. in Journal of the Ceramic Society of Japan, volume 103, pages 969-973 (1995).